There are generally four (4) main types of automotive drive line systems. More specifically, there exists a full-time front wheel drive system, a full-time rear wheel drive system, a part-time four wheel drive system, and an all-wheel drive system. Most commonly, the systems are distinguished by the delivery of power to different combinations of drive wheels, i.e., front drive wheels, rear drive wheels or some combination thereof. In addition to delivering power to a particular combination of drive wheels, most drive systems permit the respectively driven wheels to rotate at different speeds. For example, the outside wheels may rotate faster than the inside drive wheels, and the front drive wheels normally rotate faster than the rear wheels.
Drive line systems also include one or more constant velocity universal joints (e.g. plunging tripod, plunging cross groove, high speed fixed joint, etc.) where transmission of a constant velocity rotary motion is desired or required. Such joints, and their operation, are well known to those skilled in the art. Accordingly, they will be discussed only briefly below.
A plunging tripod type constant velocity universal joint is characterized by the performance of end motion in the joint. Plunging tripod joints are currently the most widely used inboard (transmission side) joint in front wheel drive vehicles, and particularly in the propeller shafts found in rear wheel drive, all-wheel drive and four-wheel drive vehicles. Plunging tripod universal joints allow their respective interconnection shafts to change length during operation without the use of splines which provoke significant reaction forces thereby resulting in a source of vibration and noise.
Another common type of constant velocity universal joint is the plunging VL or “cross groove” type, which consists of an outer and inner race drivably connected through balls located in circumferentially spaced straight or helical grooves alternately inclined relative to a rotational axis. The balls are positioned in a constant velocity plane by an intersecting groove relationship and maintained in this plane by a cage located between the two races. The joint permits axial movement since the cage is not positionably engaged to either race. As those skilled in the art will recognize, the principal advantage of this type of joint is its ability to transmit constant velocity and simultaneously accommodate axial motion. Plunging VL constant velocity universal joints are currently used for high speed applications such as, for example, the propeller shafts found in rear wheel drive, all-wheel drive and four-wheel drive vehicles.
The high speed fixed joint (HSFJ) is another type of constant velocity joint well known in the art and used where transmission of high speed is required. High speed fixed joints allow articulation to an angle (no plunge) but can accommodate much higher angles than with a Cardan joint or other non-CV joints such as, for example, rubber couplings. There are generally three types of high speed fixed joints: (1) disk style that bolts to flanges; (2) monoblock style that is affixed to the tube as a center joint in multi-piece propshafts; and (3) plug-on monoblock that interfaces directly to the axle or T-case replacing the flange and bolts.
A typical driveline system incorporates one or more of the above joints in an all wheel drive or traditional four wheel drive system. In an all wheel drive system, such joints are used to connect a pair of propeller shafts (front and rear) (also called a propeller shaft assembly) to a power take off unit and a rear driveline module, respectively. These propeller shafts (“propshafts”) function to transfer torque to the rear axle in rear wheel and all wheel drive vehicles. Similarly, in a traditional four wheel drive system, such joints are used to connect the propeller shaft between a transfer case and the front axle.
Most constant velocity universal joints are sealed in order to retain grease inside the joint while keeping contaminants and foreign matter, such as dirt, water, and the like out of the joint. In order to achieve this protection, the constant velocity joint is usually enclosed at the open end of the outer race by a sealing boot made of rubber, thermoplastic or urethane. The opposite end of the outer race is sometimes formed by an enclosed dome known in the art as a “grease cap.” Such sealing and protection of the constant velocity joint is necessary because, once the inner chamber of the outer joint is partially filled and thus lubricated, it is generally lubricated for life. Prior art seals may have imperfections between the cover and boot which may lead to leakage or contamination.
Therefore, there is a need in the art for a boot that will ensure the joint chamber is properly and effectively sealed from ingress of contaminates and leakage of lubricating grease from the joint.